Yeast stage tank incorporated fermentation system and method

ABSTRACT

Methods of and system for growing and maintaining an optimized/ideal active yeast solution in the yeast tank and fermenter tank during the fermentation filling cycle are provided. A new yeast stage tank is used between the yeast tank and the fermenter tank allowing yeast to rapidly produce a huge amount of active young yeast cells for a fermenter during the filling period. A measurable and useful controlling factor, % DT/% Yeast by weight ratio (or “food” to yeast ratio), is used (e.g., % DT=glucose), which offers information on the health status of the yeast. The controlling factor is used to control the status of the yeast throughout the entire process.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/839,763, filed Aug. 28, 2015 and titled “A FERMENTATIONSYSTEM FOR DRY MILL PROCESSES,” which claims priority to U.S.Provisional Patent Application Ser. No. 62/044,092, filed Aug. 29, 2014and titled “NEW IMPROVEMENT FERMENTATION SYSTEM FOR DRY MILL PROCESS”and this application claims priority under 35 U.S.C. § 119(e) of theU.S. Provisional Patent Application Ser. No. 62/914,276, filed Oct. 11,2019 and titled, “A YEAST STAGE TANK INCORPORATED FERMENTATION SYSTEM,”which are all hereby incorporated by reference in their entirety for allpurposes.

FIELD OF THE INVENTION

The present invention relates to the field of fermentation.Specifically, the present invention relates to the yeast conditions forthe fermentation.

BACKGROUND OF THE INVENTION

Scientists have researched and developed the use of ethanol, atwo-carbon alcohol compound, as an effective additive to gasoline tocurb the rapid usage of gasoline. In some cases, gasoline mixtures haveas high as 85% volume of ethanol as a biofuel. Although coal and oilproduce carbon dioxide from previously long-term sequestered carbon, thecarbon dioxide produced from the combustion of grain alcohol is consumedby growing the grain and quickly recycled into the environment resultingin no net carbon dioxide addition to the atmosphere, thus not leading togreenhouse gas accumulation.

In a fermentation process, ethanol and carbon dioxide are produced via abiological process, where sugar and yeast are mixed together, and thesugar is converted into cellular energy. The yeast metabolizescarbohydrates (primarily monosaccharides and disaccharides) to produceethanol (liquid) and the byproduct carbon dioxide (gas). Under carefullymoderated pH and temperature conditions to grow the yeast, thesugar-to-ethanol conversion can be up to 98% of theoretical maximum.Maximizing the yield and purity of ethanol is essential for commercialprofitability.

Fermentation is an anaerobic process that is conducted in the absence oflarge concentrations of oxygen. The formula is simple sugar (e.g.Glucose)+yeast→2C₂H₅OH (ethanol)+2CO₂ (carbon dioxide). In general,there are two types of fermentation systems in ethanol-producing moderndry mill plants. One type is continuous fermentation, which isillustrated in FIG. 1. The other type is batch fermentation, which isshown in FIG. 2. The continuous fermentation as illustrated in the FIG.1 starts in 1950s for alcohol production process for either dry mills orwet mills. Of approximately 200 dry mill plants in the U.S., about 50plants started with this continuous fermentation system. But themajority of plants have changed to batch fermentation now, even thoughcontinuous fermentation has many advantages over a batch system.

FIG. 1 illustrates a typical continuous fermentation system 100. One ortwo yeast tanks 102 about half the size of fermentation tanks 104, 106,108, 110, 112, and 114 continuously propagate yeast to supply to thefermentation tanks. In general, 6 to 12 fermenters are setup in a seriesand operate continually. The mash flow 116 is split into 3 parts. Onepart goes to a yeast tank 102 and other two go to fermenter tank #1 104and fermenter tank #2 106. (Some plants even use a third tank: fermentertank #3 108). The percentage of alcohol in the fermenter tank #1 isnormally around 5%, with alcohol content increasing faster in thebeginning and then gradually slowing by the end. The maximum percentageof alcohol in drop (after fermentation when moving to a distill tower)is normally around 12W/V (e.g., 12%/liter).

Major advantages of continuous fermentation include: a) it's a simplecontinuous operation; b) low yeast propagation costs; and c) low enzymecosts. The major disadvantages of continuous fermentation include: a)lower % alcohol in drop (after fermentation when moving to a distilltower, b) high % sugar in drop, c) it needs a longer time to start up;d) infections are very hard to stop, e) incomplete fermentation canhappen; and f) no stable condition while in operation. The lack ofcontrol over infections is the major problem in continuous fermentation:infections can happen at any time, and if an infection occurs, theinfection often wipes out all the cost savings in a very short time.This is the reason not many dry plants still use continuous fermentationin the U.S.

Instead, the majority of the 200 dry mill plants in the U.S. use thebatch fermentation process, which is shown in the FIG. 2. Batchfermentation plants run a fermentation process flow of a 30-80 hourcycle (majority are in a 50-60 hour cycle) with multiple (usuallybetween 3 and 10) fermenter tanks per facility. Yeast can be conditionedin a yeast growth tank, often called propagation tank. When the yeast inthe Yeast Propagation Tank has grown to a mature, healthy state, theYeast Solution is dumped into a Fermenter Tank. Enzyme(s) is added tothe fresh mash to convert dextrin in the mash to simple sugars.

The fermenter tank is then filled with fresh mash over a period of 5 to18 hours or until the fermenter tank is full. The fermenter tank is thenset to idle, allowing the yeast to continue to ferment sugars toalcohol. At the end of the cycle, the fermentation broth is dischargedand the Fermenter Tank is cleaned to be ready for another cycle.Fermentation cycles are normally 50 to 60 hours in dry mill plants inthe U.S. For a 4-fermenter system, filling time is around 14 hours andthe fermentation cycle is 56 hours; for a 7 fermenter tanks system,filling time is 8 hours and the fermentation cycle is 56 hours.

Over 150 dry mill plants in the U.S. operations use batch fermentation.In these plants, 100 lbs. of dry yeast are added to 2400 gallons ofyeast slurry, and water plus nutrients are added to condition the yeastfor propagating in the yeast tank. In the most common design, yeasttanks are normally 20,000 gallons, with one yeast tank for a 3 to 6fermenter system, and two yeast tanks for a 7 to 10 fermenter system.The yeast propagation time ranges from 6 hours to 11 hours, depending onthe number of fermenters in system. For example, for 4 fermenters, thefilling time is around 14 hours, and it normally needs three hours tomove the solution from the yeast tank to the fermenter tank andClean-In-Place (CIP) for next batch. So, the yeast propagation time is11 hours. For 7 fermenters, filling time is 8 hours, two yeast tanks areused (since with one yeast tank the yeast propagation time is too shortat 5 hours), with a yeast propagation time of 15 hours. The yeastpropagation rate in the yeast tank is associated with the factorsincluding the operational conditions (temperature, pH etc.), the type ofyeast used, the amount of nutrients added, and the amount of dissolvedair in the yeast tank. Yeast cells will increase at a rate of about 25to 40% per hour in the typical systems with the majority within the 30to 35% range.

SUMMARY OF THE INVENTION

The present disclosure provides systems for and methods of providingboth the yeast tank and fermenter tanks having optimized yeast cellcounts at all times. More specifically, the present disclosure providesa dual-function Yeast Stage Tank (YST) (for yeast propagation andfermentation) between the yeast tank and the fermentation tank, which isillustrated in FIGS. 3-8. In some embodiments, the yeast stage tank is aseparate tank that is between the yeast tank and the fermenter tank. Insome other embodiments, one or more fermenter tanks are used as theyeast stage tank, which has a condition configured to perform a functionas a yeast stage tank including yeast propagation such that apredetermined cell count is obtained before performing fermentation ortransferring the yeast solution to a fermenter.

The yeast stage tank of some of the embodiments supplies active youngyeast to the fermenter to maximize outcomes in the yeast propagationtank. In some embodiments, the yeast stage tank is also used as a yeastpropagation tank for yeast propagation. Fresh mash continues to feedinto the yeast stage tank and maintain an optimized yeast cell count(>250*10{circumflex over ( )}6) solution from the yeast stage tank toone or more fermenter tanks during the entire filling period. The yeaststage tank is configured to supply an optimized yeast cell solution toone or more than one fermenter tanks.

In some embodiments, the yeast stage tank is used for filling up gaps ofproviding predetermined yeasts between the yeast tank and the fermentertanks to ensure sure that the yeast cell count maintains maximum infermenter tanks during the filling period when the yeast tank is toosmall. In some embodiments, the yeast stage tank is also used as acontinue yeast propagation tank to supply a lot yeast cell to maintain amaximum yeast cell count in fermenters during the ferment fillingperiod.

The minimum yeast stage tank size is determined by a yeast propagationrate in yeast stage tank mash rate, which is summarized in TAB 4. Forexample for a 20% per hour yeast growth rate (propagation rate), thesize of the yeast stage tank must be larger than 5 (100/20=5) time ofmash rate. For a 25% per hour yeast growth rate, the yeast stage tankmust be at least 4 (100/25=4) times of mash rate. For 30% per hour yeastgrowth rate, the yeast stage tank must be at least 3.333 (100/30=3.333)time of mash rate. For 35% per hour yeast growth rate, the yeast stagetank must be at least 2.86 (100/35=2.86) times of mash rate. In otherwords, the size of the yeast stage tank can be determined using theformula of [100/% of the yeast growth] times mash rate. The average mashrate is gallon per hour (GPH) of a dry mill plant. The average mash rateis total volume of mash produce per hour for a fermentation system. Sothis average mash rate is equal to sum of mash rate that is sent toyeast tank, yeast stage tank and fermenter.

For a seven fermenter tanks system with fermenter size of 800,000 gal,the filling time is 8 hour with an average of mash rate of 100,000 galper hour. If a yeast growth (propagation) rate is 20%, 25%, 30% and 35%,the yeast stage tank shall be minimum of 500,000 gal, 400,000 gal,333,3333 gal and 285,714 gal respectively.

When larger size yeast stage tank is used, one of the fermenters can beused as a yeast stage tank first by receiving a yeast solution from theyeast tank. Next, the mash is added to a predetermined volume. Next, thefermenter tank is used as a continue yeast propagation tank (e.g., ayeast stage tank), which is used to fill up more than one fermentertanks. This continue yeast propagation can be stopped at any time, andfollowed by filling up with mash until full, which is then functioned asa typical fermenter tank by continuing to finish the process offermentation. In other words, this setup uses one of the fermenters as ayeast stage tank first. Subsequently, the yeast stage tank is used asone of the fermenter tanks later, which is able to save the costs ofusing a separate yeast stage tank but would decrease the totalfermentation capacity.

The system provides and maintains the ideal/optimized yeast cell countsolution for both the yeast tank and fermenter tank at all times. Thesystem adds a dual function (yeast propagation and fermentation) yeaststage tank between the yeast tank and the fermentation tank. This yeaststage tank supplies huge amounts of ideal/optimized yeast cell countsolution to a fermenter by a) using the yeast stage tank for continuousyeast propagation, b) recycling the ideal yeast solution from onefermenter to another fermenter, c) using both a) and b) to maintain amaximum yeast cell count (>250*10{circumflex over ( )}6) in the yeaststage tank and fermenter at all times and especially during the fillingperiod, and d) keeping the food/yeast cell ratio less than 10 (e.g., <4)at all times to avoid a) a yeast stress which produces unwanted glyceroland b) a bacterial spike which produces unwanted lactic acid. Thefood/yeast cell ratio is able to be represented by using the factor of %DT/% Yeast by weight ratio (or “food” to yeast ratio).

Further, the yeast stage tank is configured to stop at any time andfollowed by dumping the yeast solution to the fermenter tank. Such adump would be followed by a Clean-In-Place (CIP) step and then restartof another batch in the yeast stage tank. In some embodiments, enzymedosage is also controlled in the yeast stage tank to ensure thefood/yeast cell ratio is less than 5/1 to avoid a) yeast stress causedby overproduction of glycerol and/or b) bacteria out run the yeastleading to unwanted lactic acid.

An additional benefit of the yeast stage tank is the ability to providemaximized Yeast Cell Count (YCC) solution to the appropriatefermentation tank. At any point in the process, the YST (yeast stagetank) can stop filling a fermentation tank, refill with mash, and act asa fermenter tank with a significantly shorter fermentation time as shownin FIG. 8.

As mentioned above, most of the over 200 dry milling plants in the USAuse batch fermentation systems. These systems maintain 3 to 10fermentation tanks. The average fermentation cycle time is around 56hours. Normally, filling time for a 3 fermenter system is 18 hours; fora 4 fermenter system 14 hours; for a 5 fermenter system 11 hours; for a6 fermenter system 9 hours, for a 7 fermenter system 8 hours, for a 8fermenter system 7 hours, for a 9 fermenter system 6 hours, and for a 10fermenter system 5 hours. Generally an 800,000 gallon fermenter tankuses a 20,000 gallon yeast tank. For a 20,000 gallon yeast tank to fillan 800,000 gallon fermentation tank, yeast needs to propagate 40 timesduring a short filling time. Under normal conditions, yeast cell countincreases at around 30% per hour. Therefore, as shown in TAB 1, totaltime needed is 14 hours for yeast propagation time and 3 hours totransfer the yeast solution. Additionally, Clean-In-Place (CIP) timeshould be considered.

A majority of dry milling plants in the U.S. have more than 3 fermentertanks in their batch fermenter system, which are operate under a muchlower yeast cell count (<100*10{circumflex over ( )}6/ml). This loweryeast cell count creates yeast stress and produces unwanted byproductsespecially glycerol. The yeast stress also gives bacteria a chance tooutcompete the yeast and produce lactic acid. A computer simulation andfield data are used to set up the system to maintain maximum yeast cellcount in both the yeast tank and the fermenter tank. The computersimulation is based on a yeast growth rate of 20 to 35%, and alcoholproduction per cell per hour is 0.001% for yeast tank and 0.002% forfermenter tank. These numbers can change during the actual operationbased on observed fluctuations and other relevant variables. See TAB 1to TAB 3 for details.

In some embodiments, a yeast stage tank (YST) is used between the yeasttank and the fermenter tank, which is a novel and nonobvious featurethat has not been done before. In some embodiments, the yeast stage tankis larger than 3.33 times of an average mash tank/yeast tank, such thata yeast cell grow rate of 30% per hour is obtained, which is furtherconfirmed by using computer simulation calculation. See TAB 4 forvarious yeast grow rates.

At least six different embodiments are provided below illustrating someof the selected embodiments. The embodiments illustrated below allowdifferent typical dry mill plant configurations to improve productivityand reduce costs by maintaining a maximum yeast cell count at all times,which also provide advantages of decreasing yeast and enzyme costs,decreasing the chance of infection and shortening the fermentationcycle. See LT1FEM to LT6FEM on following:

LT1FEM (Split Flow Method): Mash flow is split to feed two fermentertanks at the same time, which serve as yeast stage tanks in accordancewith some embodiments. In some embodiments, the filling time doubles andthe mash flow to the fermenter tanks is controlled in the first half offilling period to obtain maximum fermenter tank yeast cell count at alltimes.

TAB 5 shows current yeast tank (20,000 gal) used as a yeast tank for a 7fermenter tanks system. TAB 6 shows an optimized yeast stage tank size(333,163 gal) used for a 7 fermenter tanks system. TAB 7 comparesalcohol percentage and yeast cell count between LT1FEM (split flowmethod) with a minimum yeast stage tank and commonly used fermentationsystems with different numbers of fermenter tanks. TAB 8 comparespercentage alcohol over time on 7 fermenter tanks systems using LT1FEMmethod with different sized yeast stage tanks. As shown, more than oneyeast stage tank in series is needed for a fermentation system with 7 ormore fermenters.

LT2FEM: (Alternating YST Method) Two yeast propagation lines are set upto alternate supplying yeast solution for a fermenter via a yeast stagetank. Multiple yeast stage tanks in series are needed for more than 6fermenter systems. This set up is ideal for switching customers from acontinuous fermentation system to a batch fermentation system.

In some embodiments, two existing large yeast tanks in continuousfermentation system are used as two large yeast stage tanks in theLT2FEM system.

TAB 9 shows two large yeast stage tanks (333,163 gal) alternating supplyfor a 7 fermenter system with 8-hour filling time. TAB 10 shows twoyeast tanks with one large yeast stage tank for a 7 fermenter systemwith LT2FEM set up. TAB 11 shows two yeast tanks plus two large yeaststage tanks are needed for a 10 fermenter system with LT2FEM system setup. TAB 12 compares alcohol percentage over time between the LT2FEMsystem and currently used fermentation systems. TAB 13 is a summary ofyeast tank sizes and yeast stage tank sizes needed for variousfermentation systems.

LT3FEM: (Continuous Yeast Propagation in YST Method) A yeast stage tank(YST) is used between the yeast tank and the fermenter tank. The yeaststage tank is used as a continuous yeast propagation tank by continuingfeeding mash in and continuing to send yeast solution out to thefermenter. This method fills up the fermenter tank without using any newyeast solution from the yeast tank. Thus, yeast propagation can continuefor more than one fermenter. When this continuous yeast propagation isused for one fermenter, the yeast propagation time in the yeast tank andthe yeast stage tank are double. When continuous yeast propagation isused for two fermenters, the time needed in the yeast tank and the yeaststage tank are triple. This decreases the capital cost and operationalcost of yeast propagation. TAB 14 shows yeast stage tank used as acontinuous yeast propagation tank for one pass (yeast solution is passedfrom one tank to the next) (to provide solution for only one fermentertank) for a 7 fermenter LT3FEM system. TAB 15 shows a yeast stage tankused as a continuous yeast propagation tank for one pass (to providesolution for only one fermenter tank) for a 10 fermenter LT3FEM system.TAB 16 compares alcohol percentage over time between the LT3FEM systemand various currently used fermentation systems. TAB 17 shows the yeasttank size and yeast stage tank size needed for LTFEM3 system.

LT4FEM: (Yeast Solution Recycling Method) A larger yeast stage tank isadded between the yeast tank and the fermenter tank. This yeast stagetank is used to produce a larger amount of the most active young yeastcells to the fermenter. This huge amount of active young yeast is dumpedto fermenter #1 (donator fermenter tank) followed by adding mash tofermenter #1 until full. The yeast stage tank used is large enough tomake sure the yeast cell count in fermenter tank #1 maintains maximumyeast cell count (>250*10{circumflex over ( )}6) during the fillingperiod. The computer simulation program further shows the yeast stagetank needs to be at least 3.33 times the mash rate for a 30% yeastpropagation rate. The minimum yeast stage tank sizes for different yeastgrowth rates are shown in TAB 4. Once fermenter #1 (donator fermenter)is full, it will continue to propagate yeast (acting as a yeast stagetank) for at least three hours by continuing to bring more mash in andsending ideal yeast solution out to fermenter tank #2 (receptorfermenter). This at least three-hour yeast solution transfer fromfermenter tank #1 (donator fermenter) to fermenter tank #2 (receptorfermenter) ensures that fermenter tank #2 will always have maximum yeastcell count (>250*10{circumflex over ( )}6) during the filling period.Next, fermenter tank #2 can start acting as a yeast stage tank byfilling with mash until full. Once fermenter #2 is full it can continueto intake mash while sending maximum yeast cell count solution toanother fermenter. This method can be continuously applied to each newfermenter maintaining an ideal yeast count during fill and then, oncefull, in-taking more mash while donating ideal yeast count solution tothe next fermenter. This method allows a recycling of the ideal yeastcell solution, ensures ideal yeast cell counts are maintained at alltimes in each fermenter, and requires significantly less enzyme. Thus,both operational and capital costs can be reduced. TAB 18 shows a 7fermenter system with a yeast stage tank and one yeast recycle pass(yeast solution passed from one fermenter to another). TAB 19 shows a 10Fermenter system with a yeast stage tank and one yeast recycle pass. TAB20 compares the alcohol percentage over time between the LT4FEM systemand currently used 7 and 10 fermenter systems. TAB 21 shows the size ofthe yeast tank and yeast stage tank needed for a LT4FEM system.

LTSFEM: (Continuous Yeast Propagation in YST or Fermenter Method) Thissystem combines the continuous propagation of active yeast solution in ayeast stage tank used in LT1, LT2, and LT3 methods with the recyclingmethod of LT4FEM. LTSFEM uses a yeast stage tank to provide hugequantities of active young yeast cells to more than one fermenter byusing a yeast stage tank as a continuous yeast propagating tank (LT3FEM)or using a fermenter as a continuous yeast propagation tank (LT4FEM).With this system, there are many ways to set up an optimum yeastpropagation system for batch fermentation. TAB 22 shows the minimum sizeof a yeast stage tank needed for various systems. TAB 23 shows asimulation for a 7 fermenter system using one yeast stage tank forcontinuous yeast propagation and using a minimum size yeast stage tankfor one yeast recycle pass (yeast solution passed from one fermenter toanother). TAB 24 shows a simulation for a 7 fermenter system using oneyeast stage tank for continuous yeast propagation and using a maximumsize yeast stage tank for one yeast recycle pass. TAB 25 shows asimulation for a 10 fermenter system using one yeast stage tank forcontinuous yeast propagation and another for yeast recycle pass withLTSFEM system. TAB 26 shows a simulation for a 10-fermenter system usingtwo yeast stage tanks for yeast recycling. TAB 27 shows a simulation ofa 10 fermenter system using two yeast stage tanks for continuous yeastpropagation.

LT6FEM: (Fermenter Tank used as YST Method) The above systems (LT1FEM,LT2FEM, LT3FEM, LT4FEM, and LTSFEM system) need to a) add an additionalyeast stage tank to the existing system, b) dump yeast solution tofermenter, and c) Clean-in-Place (CIP) the yeast stage tank. These needsadd capital cost and operational cost. LT6FEM system is developed byusing one fermenter as a yeast stage tank. This yeast stage tank cancontinuously propagate yeast by adding mash to the tank while sendingmaximized yeast cell count solution to a fermenter. This yeast stagetank, which is continuously propagating yeast, can fill multiplefermenters with ideal yeast cell count solution. At any time this tankcan stop yeast propagation and act as an additional fermenter by fillingwith mash and stopping donation of yeast solution to another fermenter.During this time, another fermenter tank can begin acting as a yeaststage tank. This way, the first yeast stage tank fills up with mash tobecome a fermenter and the next fermenter starts acting as a yeast stagetank. Using this strategy all yeast stage tanks and fermentersconsistently maintain maximum yeast cell counts (>250*10{circumflex over( )}6) during the filling period. Thus, the alcohol percentage (whichstarts around 2%) will gradually increase and not create any suddenalcohol percentage changes when the yeast solution is passed from onefermenter to another (recycle pass) as seen in the LT4FEM system. Usingthis continue yeast propagate in yeast stage tank technique, the LT6FEMsystem will increase alcohol percentage from 2% up to 6% during thefilling period and reach a maximum of 0.5% per hour rate. Thus, LT6FEMcan operate on a 48-hour (two days cycle) fermentation cycle instead ofthe currently used 56-hour fermentation cycle. TAB 28 shows LT6FEM usingone recycling pass with each fermenter in the system taking turns actingas a yeast stage tank (propagating yeast and feeding next fermenter) fora 4 fermenter system with a 16-hour filling time. TAB 29 shows summaryof the LT6FEM system with various fermentation systems. TAB 30 show asummary of alcohol percentage in fermenter using LT6FEM system. TAB 31shows the minimum size of a yeast tank needed for a LT6FEM system. TAB32 shows the minimum size of a yeast stage tank needed for a LT6FEMsystem. TAB 33 shows the average alcohol percentage at hour 18 with aminimum size yeast tank. TAB 34 shows the decrease in fermentation timewith a minimum size yeast tank. TAB 35 shows the pounds of dry yeastneeded with a minimum size yeast tank. TAB 36 compares yeast cell countand alcohol percentage between currently used systems and an LT6FEMsystem for a 7 fermenter system. TAB 37 shows a summary of alcoholpercentage after 18 hours after multiple recycling passes (fermenter tofermenter yeast solution transfer) using the LT6FEM method for a 7fermenter system.

Use of a larger yeast stage tank provides more stable operation (allowslower yeast growth rate and a shorter fermentation cycle). But a largeryeast stage tank requires more spaces to accommodate the larger yeasttank. For all batch systems, the maximum size yeast stage tank operationcapacity will be the same as the fermenter capacity. TAB 38 shows thesize of yeast tanks needed for various yeast growth rates with a maximumsize yeast stage tank in a LT6FEM system. TAB 39 shows the averagealcohol percentage at hour 18 for various yeast growth rates withmaximum size yeast stage tank on LT6FEM system. TAB 40 shows thedecrease in fermentation time due to the use of a maximum size yeaststage tank for various yeast growth rates on LT6FEM system. TAB 41 showsthe amount of dry yeast needed for a maximum size yeast stage tank withvarious yeast growth rates on LT6FEM system. A comparison of minimumsize yeast stage tank data (TAB 31 to TAB 35) with maximum size yeaststage tank data (TAB 38 to TAB 41) shows that there are many differentways for a customer to improve operational conditions and decrease costsby using LT6FEM technology to optimize their fermentation system.

This computer simulation program also can be used to aid the design ofnew fermentation systems. All of the computer simulation data shows thatsystems with fewer fermenter numbers (4 to 6) and longer filling times(9 to 16 hour) cost less and perform better than fermentation systemswith more fermenters (7 to 10) and shorter filling times (5 to 8 hour).The computer simulation data demonstrates that existing larger number (7to 10) fermentation systems can be turned into two better performingfermentation systems. For example, a 8 fermenter system with 7 hourfilling time can be made into two 4 fermenter systems with 14 hourfilling times. Similarly, a 10 fermenter system with 5.5 hour fillingtime can be made into two five fermenter systems with filling times of11 hours as shown in TAB 30.

The computer simulation program is a very useful and valuable tool fordesigning new fermentation systems and for improving current systemoperation. The simulation can a) analyze the field data, b) find thelocation of abnormal operation or inefficiency, c) model variousmodifications to the system, and d) compare different fermentationmodifications. This allows new fermentation systems to be optimallydesigned and existing systems to be optimized for cost and performance.Generally, one small mistake in actual field operation can lead to ahuge loss in profit. In addition, a single day of computer simulationcan provide more useful data than hiring a fermentation specialist tocollect data in the field for decades.

In the following, some experimental data are provided in accordance withsome embodiments. TAB 1 shows some important yeast propagation methodsand data. The right yeast tank has been designed depending on the yeastpropagation time in the system. Plot 1-1 shows the yeast cell increaseratio as a function of yeast propagation with various yeast propagationrates (from 0.25 to 0.4). The yeast propagation time has been used todesign an ideal yeast tank propagation system. The percentage of alcoholin the yeast tank versus time is also plotted in Plot 1-2 using acomputer simulation with various alcohol production rates (0.001% to0.0015% alcohol produced per yeast cell per hour). This number dependson the type of yeast, yeast tank conditions (pH temperature and nutrientetc.) and most importantly, the dissolved air inside the yeast tank.Normally, plants only have yeast propagation data at the end of yeastpropagation. However, those two plots are very useful for understandingand designing a yeast propagation system that considers limitingfactors, how to improve results, and what to expect with all possibleimprovement options. These two plots are able to be used to guide designand the operation of the yeast tank to maximize yeast cell count withthe most active (high % budding and viability) young yeast for thefermenter tanks.

A computer simulation program shown in TAB 2 (for a current 7-fermentersystem) is based on 100 lbs. of dry yeast in a 2400 gallon yeast slurrytank, then transferred to a 20,000 gallon yeast tank for a 16 hour yeastpropagation cycle in the yeast tank to produce 20,000 gallons of activeyoung yeast which are then transferred to a 800,000 gallon fermentertank. With a mash rate of 100,000 gallons per hour, the fermenter tankwill take 8 hours to fill up. As shown in TAB 2, the yeast cell countremains very low during this 8-hour filling period, as it takes 14 hoursto reach the maximum yeast cell count. Similarly, the data shows a15-hour lag period for alcohol production. The glucose in the fermentertank also gradually increases from about 1% to as high as 14% duringthis period. This high glucose and low yeast cell count period createsyeast stress and produces the unwanted byproduct glycerol. The datashows that the percentage of glycerol increases from around 0.5% to ashigh as over 1% during this period with regular dry yeast. Some recentlyreleased GMO yeasts can decrease the percentage of glycerol to less than1% and increase alcohol yields up to 2.5%.

The same computer simulation program is used for 4 to 10 fermenters inthe current fermentation systems and is summarized in TAB 3. Yeast CellCounts (YCC) in the fermenters start very low (93*10{circumflex over( )}6 for a 4 fermenter system, 76*10{circumflex over ( )}6 for a 5fermenter system, 39*10{circumflex over ( )}6 for a 6 fermenter system,54*10{circumflex over ( )}6 for a 7 fermenter system, 48*10{circumflexover ( )}6 for a 8 fermenter system, 42*10{circumflex over ( )}6 for a 9fermenter system and 27*10{circumflex over ( )}6 for a 10 fermentersystem), so the yeast in the fermenter is under stress during and afterthe filling time: 14 hours for a 4 fermenter system, 15 hours for a 5fermenter system, 16 hours for a 6 fermenter system, 15 hours for a 7, 8and 9 fermenter system, and 16 hours for a 10 fermenter system. Incontrast, a typical system spends more than 14 hours with a low yeastcell count (less than 250*10{circumflex over ( )}6). The low yeast cellcount stresses the yeast causing glycerol production, which slows thealcohol production rate for more than 14 hours.

Normally, improving this fermentation system requires a big capitalinvestment, additional operational costs, and longer development time.This computer simulation program provides a much quicker, lessexpensive, and easier way to develop new fermentation technology, sincemany possible improvements can be tried in the computer simulationprogram and results compared prior to adjusting the system.

As described in the provisional Patent Application Ser. No. 62/044,092,filed Aug. 29, 2014 and titled, “NEW IMPROVEMENT FERMENTATION SYSTEM FORDRY MILL PROCESS,” recycling yeast from a donating fermenter to areceiving fermenter can keep the yeast cell count at a maximum(>250*10{circumflex over ( )}6) for all receiving fermenters, andproduce less glycerol (as low as 1.1%) are all incorporated byreferences for all purposes. However, the yeast cell count in thedonating fermenter is still very low and the percent of glycerol in thedonating fermenter may be as high as 1.5%.

In addition, a measurable and useful parameter, % DT/% Yeast by weightratio (or “food” to yeast ratio), is also introduced. (e.g., %DT=glucose) This ratio offers information on the health status of theyeast after every hour and a method of smoothly transferring the yeastfrom yeast-growing phase to alcohol producing phase during a fermenterfilling period, such that shocks to the yeast are able to be avoided.Because the yeast cell count in the donating fermenter is still verylow, bacteria has time to get a foothold in the donating fermenter andto be transferred to the receiving fermenter, creating a chance thatbacteria outruns yeast in the donating fermenter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of examples, with reference tothe accompanying drawings which are meant to be exemplary and notlimiting. For all figures mentioned herein, like numbered elements referto like elements throughout.

FIG. 1 illustrates a typical continuous fermentation system.

FIG. 2 illustrates a typical batch fermentation system.

FIG. 3 illustrates a mash split flow process in accordance with someembodiments.

FIG. 4 illustrates alternating yeast tanks as a yeast stage tank processin accordance with some embodiments.

FIG. 5 illustrates a continuous yeast propagation in a YST in accordancewith some embodiments.

FIG. 6 illustrates a yeast solution recycling process in accordance withsome embodiments.

FIG. 7 illustrates a continuous yeast propagation in YST or a fermentertank in accordance with some embodiments.

FIG. 8 illustrates using a fermenter tank used as a YST in accordancewith some embodiments.

FIG. 9 illustrates using a fermenter tank used as a YST in accordancewith some embodiments.

FIG. 10 illustrates using a fermenter tank used as a YST in accordancewith some embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made in detail to the embodiments of the present invention,examples of which are illustrated in the accompanying drawings. Whilethe invention is described in conjunction with the embodiments below, itis understood that they are not intended to limit the invention to theseembodiments and examples. On the contrary, the invention is intended tocover alternatives, modifications and equivalents, which can be includedwithin the spirit and scope of the invention as defined by the appendedclaims. Furthermore, in the following detailed description of thepresent invention, numerous specific details are set forth in order tomore fully illustrate the present invention. However, it is apparent toone of ordinary skill in the prior art having the benefit of thisdisclosure that the present invention can be practiced without thesespecific details. In other instances, well-known methods and procedures,components and processes have not been described in detail so as not tounnecessarily obscure aspects of the present invention. It is, ofcourse, appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application and business-related constraints, and that thesespecific goals vary from one implementation to another and from onedeveloper to another. Moreover, it is appreciated that such adevelopment effort can be complex and time-consuming but is neverthelessa routine undertaking of engineering for those of ordinary skill in theart having the benefit of this disclosure.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding ofprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It is readilyapparent to one skilled in the art that other various modifications canbe made in the embodiment chosen for illustration without departing fromthe spirit and scope of the invention as defined by the claims.

LIST OF TABLES OF COMPUTER SIMULATION DATA

-   TAB 1: Batch method yeast propagation theory and data.-   TAB 2: Computer simulation for a current ICM 7 fermenter system with    two 20,000 gallon yeast tanks.-   TAB 3: Summary of results on all current ICM batch fermentation    systems (from a 4 fermenter system to a 10 fermenter system) by    computer simulation.-   TAB 4: Shows minimum yeast stage tank size required to maintain    maximum yeast cell count.-   TAB 5: Computer simulation for a 7 fermenter system with LT1FEM    (split mash flow method).-   TAB 6: Computer simulation showing optimum (maximum) yeast stage    tank size (333,163 gallon) for a 7 fermenter system with LT1FEM.-   TAB 7: Compares results between current ICM systems and LT1FEM    system.-   TAB 8: Compares alcohol percentage over time for a 7 fermenter    system with various yeast stage tank sizes with LT1FEM setup.-   TAB 9: Computer simulation for a 7 fermenter system with LT2FEM    system.-   TAB 10: Other set up for a 7 fermenter system with LT2FEM system.-   TAB 11: Computer simulation for a 10 fermenter system with LT2FEM    system.-   TAB 12: Compares results between LT2FEM system and current ICM    systems.-   TAB 13: Shows yeast stage tank size, yeast tank size, and dry yeast    need for LT2FEM system.-   TAB 14: Computer simulation for 7 fermenters with LT3FEM system.-   TAB 15: Computer simulation for 10 fermenters with LT3FEM system.-   TAB 16: Compares results between LT3FEM and current ICM systems.-   TAB 17: Shows yeast stage tank size, yeast tank size and amount of    dry yeast needed for LT3FEM system.-   TAB 18: Computer simulation for a 7 fermenter system with LT4FEM    system.-   TAB 19: Computer simulation for a 10 fermenter system with LT4FEM    system.-   TAB 20: Compares alcohol percentage over time between LT3FEM, LT4FEM    and current ICM setup for 7 and 10 fermenter systems.-   TAB 21: Shows amount of dry yeast, yeast tank size, and yeast stage    tank for LT4FEM system with various number of fermenters.-   TAB 22: Summary of minimum yeast stage tank size need for LT2FEM,    LT3FEM and LT4FEM systems.-   TAB 23: Computer simulation for a 7 fermenter system with one yeast    stage tank as continuous yeast propagation tank and one yeast    recycle pass with minimum size yeast stage tank.-   TAB 24: Computer simulation for a 7 fermenter system with one yeast    stage tank as continuous yeast propagation tank and one yeast    recycle pass with maximum size yeast stage tank (same size as    fermenter).-   TAB 25: Computer simulation for a 10 fermenter system with one pass    of continuous mash intake and continuous yeast propagation to    fermenter and one yeast recycle pass setup.-   TAB 26: Computer simulation for a 10 fermenter system with two    recycle passes setup.-   TAB 27: Computer simulation for a 10 fermenter system with two    continuous yeast propagation passes (yeast solution transfers from    yeast stage tank to fermenter).-   TAB 28: Computer simulation program for a LT6FEM system.-   TAB 28A: Compares alcohol percentage over time between LT6FEM and    currently used 4 fermenter systems.-   TAB 29: Summary of LT6FEM results for use of one fermenter as Yeast    Stage Tank and then fermentation operation.-   TAB 30: Alcohol percentage in fermenters over time at the 18 hour    mark with a minimum yeast stage tank size for a LT6FEM system.-   TAB 31: Yeast tank capacity needed for a minimum yeast stage tank    size for a LT6FEM system.-   TAB 32: Minimum yeast stage tank capacity needed.-   TAB 33: Average % Alcohol at hour 18 with a minimum yeast stage tank    size.-   TAB 34: Decrease in fermentation time with a minimum yeast tank    size.-   TAB 35: Pounds of dry yeast needed with a minimum yeast stage tank    size.-   TAB 36: Summary of alcohol percentage for a 7 fermenter system with    an LT6FEM system.-   TAB 37: Summary of results for a 7 fermenter system with multiple    passes using the LT6FEM System.-   TAB 38: Summary for yeast tank/mash rate needed for a maximum yeast    stage tank.-   TAB 39: Average alcohol percentage at hour 18 mark for a maximum    yeast stage tank.-   TAB 40: Decrease in fermentation time with a maximum yeast stage    tank.-   TAB 41: Pounds of dry yeast needed for a maximum yeast stage tank.-   TAB 42: Optimum fermentation design system.

For a small tank, 100 pounds of dry yeast are used in a yeast slurrytank, which fills with 2400 gallons of water to form a yeast solutionwith a yeast cell count of 250*10{circumflex over ( )}6. To maintainthis ideal yeast count for an 800,000 gallon fermenter tank, thequantity of yeast should increase by 333 times. When a 20,000 gallonyeast tank is used, the initial 100 pounds of yeast is multiplied 8.3times to fill the yeast tank with the optimized yeast cell countsolution. Then the 20,000 gallons of yeast solution should multiplyanother 40 times to fill the fermenter. Current batch fermenter systemsincluding ICM's have too small a yeast tank, which increases yeastpropagation time and lengthens the fermentation cycle.

Larger yeast tanks also need more time for yeast propagation beforesending the yeast solution to a fermenter. For one yeast tank systems,the yeast tank only has one filling time to propagate the yeast. Twoyeast tank systems can create twice as much yeast solution in the yeasttanks thus cutting in half the time to fill fermenters. This is whylarger scale fermenter systems (7 or more fermenters) use two yeasttanks. For example, 10 fermenter systems, the filling time needs only 5hours. Two yeast tank systems will give 10-hours of yeast propagationtime. Accounting for three hours of moving the solution to the fermenterand

Clean-In-Place (CIP) time, the yeast propagation time only is left with7 hours, in which time the yeast can only grow 6.27 times with a yeastgrowth rate of 30% per hour. Therefore, multiple yeast tanks in seriesare needed for 9 or more fermenter systems.

Fermentation is a complex system with living organisms. The finalresults always differ even when systems and operations appear identical.However, the computer simulation, in accordance with some embodiments,are used to analyze the problems, model numerous setup systems, andcompare the results. Based on these results, any batch fermentationsystem can be optimized. The computer simulation used in this disclosureis based on following principles:

-   -   a) Yeast propagation rate per hour: Using field data as a basis,        the yeast propagation rate per hour depends on the type of yeast        used, yeast tank conditions (pH, temperature, etc.), the        nutrients inside the yeast tank, and the amount of dissolved air        in the yeast tank. The normal dissolved air levels range from 25        to 40% with most in the 30% range. Thus, 30% dissolved air is        used in the computer application.    -   b) The alcohol production rate per hour: Using field data as a        basis, the alcohol production rate in the yeast tank and        fermenter tank are a function of yeast type, yeast tank and        fermenter tank conditions (pH, temperature, etc.), nutrients in        the yeast and fermenter tanks, and the amount of air in the        yeast tank. The normal range of alcohol production is between        0.001% and 0.0015% alcohol per yeast cell per hour for the yeast        tank and 0.002% alcohol per yeast cell per hour for the        fermenter. Thus, 0.001% for the yeast tank and 0.002% for the        fermenter tank are used as baselines in this disclosure.        However, this variable can be adjusted in the computer program        and can be used to better optimize fermentation systems.    -   c) The optimized/targeted yeast cell count in the field varies        from 250 to 350*10{circumflex over ( )}6/ml. For purposes of        this disclosure, an ideal yeast cell count of 250*10{circumflex        over ( )}6 is used.

In some embodiments, a computer simulation is used based on the aboveprinciples/assumptions for 7 fermenter systems currently used by ICMsystems as shown in TAB 2. The cell A2:U3 shows all the input data forsubsequent calculations. All the numbers in red font can be adjustedbased on existing system parameters or desired outcomes. The yeast tanks(A and B) calculations are shown in cell B4: K24. The fermentationcalculation for fermentation tanks 1 and 2 are shown in cell L4:U24. Thenumber projected by the computer simulation for both yeast cell countand alcohol percentage in the yeast tank and fermenter tank areextremely consistent with field data. Plot 2-1 and plot 2-2 show theyeast cell count in fermenter tanks below 60, and an alcohol percentagein fermenter tanks below 0.5% during the filling period (less than 8hours).

Under these conditions (low yeast cell count and low alcohol percentage,there is a chance for either yeast to become stressed and produceunwanted byproducts (glycerol) or for bacteria to outgrow the yeast andproduce unwanted byproducts (lactic acid). The data confirms a sharpincrease in both the bacterial count and percentage of glycerol in thefermenter during the first 20 hours. The plot shows that maximum YCC(yeast cell count) 250*10{circumflex over ( )}6 is not reached untilhour 14. This means that there are 14 hours of lag time before alcoholproduction rates are ideal.

Using the same methodology, computer simulations are also used for otherbatch fermenter systems (4 to 10 fermenter systems). The YCC over timeand the alcohol percentage over time are shown in TAB 3. This clearlyshows that yeast cell counts in all of these systems are low during thefilling period. YCC reaches a maximum (250*10{circumflex over ( )}6) athour 14 for 4 and 5 fermenter systems, at hour 15 for 7, 8 and 9fermenter systems, and hour 16 for 6 and 10 fermenter systems. Thecomputer simulation data is consistent with field data. The alcoholpercentage in these fermenters is all well below 1.5% during filling andlead to an alcohol production lag time of 14 to 16 hours. Ideal alcoholproduction is not reached until the yeast cell count reaches a maximum(>250*10{circumflex over ( )}6), which takes between 14 to 16 hours asshown.

In some embodiments, a computer simulation program is used to performand/or optimize fermentation systems to maintain a maximum YCC in bothyeast tanks and fermenter tanks. When a maximum YCC is maintained duringand after the filling period, bacterial growth and yeast stress can beavoided. In addition, alcohol production has a significantly shorter lagtime. Following are some of the methods used:

FIG. 3 illustrates a mash split flow method 300 in accordance with someembodiments. In some embodiments, the method 300 splits the mash to feedtwo fermenter tanks. In some embodiments, two 20,000 gallon yeast tankswork in parallel to dump more than 35,500 gallons of propagated yeast tothe fermenter every 8 hours, such that the yeast cell count in thefermenter remains ideal/optimized. In some embodiments, two yeast tanksof more than 35,500 gallons (e.g., larger yeast tanks) are installed,which are able to be operated on a 16-hour yeast propagation cycle. Insome embodiments, the larger yeast tank has a size greater than 30,000gallon yeast tank.

LT1FEM: (Split Flow Method) Using this method, mash flow 302 is split tofeed two fermenters 306 and 308. The first fermenter 306 is filled tomaintain a maximum yeast cell count as shown in TAB 5 for a 7 fermentersystem with a 20,000 gallon yeast tank. Fermenter tanks 310 are tanks #3to #6 that are used for performing fermentation processes.

In some embodiments, two yeast tanks (A&B) with 16-hour yeastpropagation cycles can supply yeast solution to a fermenter every 8hour. The mash rate to fermenter #1 306 is shown in cell I7:I22. Thealcohol percentage in fermenter #1 306 is shown in cell K7: K22, and theYCC in fermenter #1 is shown in cell J7: J22.

The YCC (yeast cell count) in the fermenter is below maximum until hour9 to 11, because the yeast tank is too small. In some embodiments, two20,000 gallon yeast tanks work in parallel to dump more than 35,500gallons of propagated yeast to the fermenter every 8 hours, the yeastcell count in the fermenter remains ideal. This two yeast tank methodneeds 200 pounds of dry yeast every 8 hours. To cut down dry yeastcosts, two yeast tanks with more than 35,500 gallons can be installedand can operate on a 16-hour yeast propagation cycle. TAB 6 shows thisby changing the 19,990 gallons in cell L6 to 39,980 gallons. With thenew larger yeast tanks, only 49 pounds of dry yeast is needed every 8hours. TAB 6 shows the optimum yeast tank size for 7 fermenter systemsusing the LT1FEM setup. TAB 7 compares LT1FEM and typical ICM systemswith regard to YCC over time and alcohol percentage over time. LT1FEM(split flow method) can maintain a maximum YCC in the fermenter if theyeast tank has the optimum size. The ideal yeast tank size forfermentation systems with different numbers of fermenters is shown incell B35:H35 in TAB 7. TAB 8 shows alcohol percentage over time for 7fermenter systems with various yeast tank sizes. Advantageously, usingtwo larger yeast tanks can decrease lag time for alcohol production andalso use less dry yeast than smaller tanks. Typical ICM fermentationsystems with 4, 5, 6 and 7 fermenters with 20,000 gallon yeast tanks areideal for using the LT1FEM method. To modify, these systems just need toadd control valves for the mash flow to the fermenters. For fermentersystems with 8 or more fermenters, other solutions (LT3FEM, LT4FEM orLTSFEM) are detailed later.

FIG. 4 illustrates a method 400 having alternating two or more yeasttank system in accordance with some embodiments. In some embodiments,there are two yeast propagation lines from a tank with dry yeasts tosend a yeast solution to fermenters, which can be having two yeast tanksfollow by one yeast stage tank. Alternatively, one yeast tank followedby two yeast stage tanks or two yeast tanks followed by two yeast stagetanks are other alternatively embodiments.

The numbers of yeast tanks and/or yeast stage tanks are able to bedetermined by the numbers of fermenter tanks and system operationalconditions.

In some embodiments, the two-line yeast propagation system has one linesending the yeast solution to one or more of the fermenter tanks, andthe other line starts to prepare new yeast solution for the next cycleof fermentation. This two-lines setup is able to operate alternately tosupply a yeast solution to the fermenter tanks.

LT2FEM: (Alternating YST Method) This method 400 uses either two largeyeast stage tanks (333,163 gallons) or two yeast tanks 402 and 404(78,748 gallon) and one yeast stage tank 406 (292,384 gallon) topropagate yeast and feed yeast solution to fermenters 408. TAB 9 showssimulation data for a 7 fermenter system using LT2FEM system/technologywith two large yeast stage tanks. Two large yeast stage tanks (333,163gallons) each with a 16 hour cycle alternate providing yeast solution toa fermenter. Thus, the fermenter receives solution every 8 hours and canmaintain a maximum YCC (>250*10{circumflex over ( )}6) during thefilling period, see cell J7:J14. Using this method, 458 pounds of dryyeast are needed every 8 hours. TAB 10 shows simulation data for a 7fermenter system with two yeast tanks (78,748 gallon) and one largeyeast stage tank (292,384 gallon).

With this solution, enough yeast is propagated to maintain a maximumyeast cell count (>250*10{circumflex over ( )}6) in a fermenter duringthe filling period. 106 pounds of dry yeast is added to 2600 gallons ofwater in the yeast slurry tank, then this wet/reactive yeast with amaximum YCC is sent to a 78,748 gallon yeast tank (yeast tank A or B).The mash is gradually added to the yeast tank by controlling valves asshown in cell C13: C25 to ensure ideal YCC in the yeast tank.

Using a 16 hour yeast propagation cycle, at hour 13, the 78,748 gallonsof active young yeast are sent to the yeast stage tank (292,384 gallons)to continue yeast propagation. The two yeast tanks (402 and 404) areoperated on 13-hour yeast propagation time. Mash is gradually added andsolution is sent to the yeast stage tank 406 at hour 13 and followed byClean-In-Place (CIP) of the 78,748 gallon yeast tank 406. It takes 3hours to send the yeast solution and CIP the yeast tank. Thus, yeasttanks 402 and 404 have a 16 hour yeast propagation cycle. The yeasttanks 402 and 404 alternately send yeast solution to the yeast stagetank 406, so the yeast stage tank 406 receives yeast solution every 8hours. The yeast stage tank has a 8 hour yeast propagation cycle (5hours to propagate yeast and 3 hours to send yeast solution to thefermenter and perform CIP). Thus, every 8 hours, the yeast stage tankreceives yeast solution from yeast tanks 402 or 404 (alternating).

Mash is added to the yeast stage tank by using controlling valves (seecell I10:I14) to maintain maximum yeast cell count in the yeast stagetank 406 at all times. After 5 hours of yeast propagation in the yeaststage tank 406, the 292,384 gallons of active young yeast in solutionare sent to a fermenter tank 408. This happens every 8 hours as theyeast stage tank needs 5 hours of propagation time and 3 hours to dumpand CIP. After receiving 292,384 gallons of active young yeast solution,the fermenter 408 continues to add mash at an average mash rate of100,000 gallons per hour. Cell L7:L14 shows the fermenter status after 8hours. The YCC in the fermenter tank (see cell M7: M14) is always at amaximum (>250*10{circumflex over ( )}6). The alcohol percentage in thefermenter is shown in cell N7:N14. Compared with currently used ICMfermentation systems,

Advantageously, the LT2FEM can decrease the fermentation cycle by about8 hours. Thus, by using LT2FEM technology, a fermenter system cancomplete a full fermentation cycle in 48 hours instead of 56 hours,which increases system efficiency by over 14 percent and is simpler foran operator to control.

As explained, the LT2FEM system uses either two yeast stage tanks(333,163 gallons) (See TAB 9) or two yeast tanks (78,748 gallons) withone larger yeast stage tank (292,384 gallons) (See TAB 10). The secondmethod (TAB 10) only uses 108 pounds of dry yeast every 8 hours comparedwith the 458 pounds needed by the two yeast tank set up shown in TAB 9.As shown in TAB 11, a 10 fermenter system needs 417 pounds of dry yeasteach time, two 10,000 gallon yeast slurry tanks, two 62,749 gallon yeasttanks, and two 393,738 gallon yeast stage tanks, see cell B4:M22. TAB 12compares alcohol percentage overtime using typical ICM systems and theLT2FEM method. LT2FEM cuts fermentation time by 8 to 10 hours (8 hoursfor 7 fermenter systems, and 10 hours for 10 fermenter systems). TAB 13shows the amount of dry yeast, size of the yeast tank, and size of theyeast stage tank for optimized 4 to 10 fermenter systems using thismethod. This LT2FEM system uses additional yeast and yeast stage tanksbut decreases total fermentation cycle time by up to 10 hours. Thissolution is perfect for converting a continuous fermentation system to abatch fermentation system as most continuous fermentation systemsalready have two large yeast tanks which can be used as yeast stagetanks as shown in TAB 9.

FIG. 5 illustrates a method 500 having a Continuous Yeast Propagation ina YST in accordance with some embodiments. The method 500 is embodied asLT3FEM: (Continuous Yeast Propagation in YST Method). This method 500system uses a large yeast stage tank 504 to continuously propagate yeastand supply yeast solution from a yeast tank 502 for one or morefermenters 506. The yeast stage tank 504 can dump an ideal/optimized YCCsolution to any selected fermenter tank 506. TAB 14 shows simulationdata for a 7 fermenter system with an LT3FEM set up.

For LT3FEM, 121 pounds of dry yeast is added to 2900 gallons of water inthe yeast slurry tank for two hours and then dumped to a yeast tank(87,834 gallon). The yeast tank is filled up with mash at a controlledmash rate (see cell C6:C23) to maintain an ideal YCC (>250*10{circumflexover ( )}6) during the filling period. Yeast propagates in the yeasttank for 16 hours before dumping the yeast solution to a 326,122 gallonyeast stage tank. Mash rate to the yeast stage tank is controlled forthe next 16 hours to maintain a maximum YCC (>250*10{circumflex over( )}6) (see cell F6:F23). The yeast stage tank can then be used topropagate more yeast by adding mash at a controlled rate while feedingoptimized/ideal YCC solution to a fermenter (see cell (K6:K22). Withthis method, the YCC in the fermenter is always at a maximum YCC duringthe filling period (see cell I6: I23), and the likelihood of yeaststress or bacterial spikes are greatly decreased.

As soon as the first fermenter of the fermenters 506 is filled, theyeast stage tank 504 can start dumping to another fermenter 506 whilestill continuing to intake mash 508. This continuous cycle of intakingmash 508 to the yeast stage tank 504 and sending ideal YCC solution tothe next fermenter 506 without adding more dry yeast can continueindefinitely (See cell P15:P22).

TAB 14 shows simulation data for a 7 fermenter system using an LT3FEMsystem and TAB 15 shows data for a 10 fermenter system using an LT3FEMsystem. For the 10 fermenter system, yeast propagation time decreases to10 hours using LT3FEM technology, so extra yeast propagation tanks(7,400 gallon yeast slurry tank, 46,434 gallons of the 1^(st) yeasttank, 291,306 gallons of the 2^(nd) yeast tank, and 492,400 gallons of ayeast stage tank are needed to maximize yeast cell counts to fermentersin a 10 fermenter system. In TAB 15, see cell B4:D19 for 1^(st) yeasttank (46,434 gallon) operation data, see cell E4:G19 for 2nd yeast tank(291,360 gallon) operation data, and see cell H4:L19 for yeast stagetank (492,408 gallon) data.

Comparing TAB 10 using LT2FEM with Tab 14 using LT3FEM for 7 fermentersystems and TAB 11 using LT2FEM with TAB 15 using LT3FEM for 10fermenter systems, it is clear that the alcohol percentage productioncurve is about the same, but LT3FEM requires only one yeast tank anddecreases yeast propagation costs. Thus, LT3FEM outperforms LT2FEM bycutting capital and operational costs. TAB 16 compares alcoholpercentage over time between LT3FEM and currently used ICM systems. Thisshows the alcohol percentage using LT3FEM can be achieved with a 48 hourfermentation cycle. In contrast, the typically used ICM systems require58 hours. TAB 17 summarizes yeast stage tank size, yeast tank size,yeast slurry tank size, and the amount of dry yeast needed for variousfermentation systems (4 fermenter to 10 fermenter).

FIG. 6 illustrates a method 600 having a Yeast Solution Recycling systemin accordance with some embodiments. The method 600 is embodied asLT4FEM (Yeast Solution Recycling Method), which provides an advantage ofmaintaining a maximum yeast cell count at all three tanks (yeast tank602, yeast stage tank 604, and the fermenters 608).

The method 600 combines at least one large yeast stage tank 604 andcycles yeast 610 from one fermenter to the next fermenter of thefermenters 608. This way both yeast stage fermenter 604 and thefermenter tank 606 maintain ideal YCC during the filling period. TAB 18shows simulation data for a 7 fermenter system with yeast solutioncycled from fermenter #1 606 to fermenter #2 608A. This setup requires14.6 pounds of dry yeast to be added to 350 gallons of water in theyeast slurry tank for two hours and then dumped to a 10,601 gallon yeasttank for a 16 hour yeast propagation cycle. During the yeast propagationcycle mash intake is controlled to maintain a maximum YCC while filling(See cell C13:C25). Once full, the yeast tank 602 dumps to a 321,067gallon yeast stage tank 604 where mash 612 intake is adjusted tomaintain a maximum YCC until the yeast stage tank 604 is full (see CellF10:F22). The yeast stage tank 604 then sends ideal yeast solution tofermenter #1 606. The fermenter #1 606 continues to intake mash 612maintaining the ideal YCC at all times (See cell K7:K14). Once fermenter#1 606 is full it can send yeast solution to fermenter #2 608A for threehours while continuing to intake mash 612. After three hours, mash flowswitches to filling fermenter #2 608A until full while maintaining anideal YCC. Using this solution, two fermenters are able to use the yeastsolution from one yeast stage tank 604.

TAB 18 shows simulation data for a 7 fermenter system with this recyclesystem (yeast solution continuously transferred from one fermenter tothe next) set up using a yeast tank (10,601 gallons) and a 321,067gallon yeast stage tank. TAB 19 shows simulation data for a 10 fermentersystem using LT4FEM. Because the filling time is only 5 hours for 10fermenter systems, two yeast tanks (11,922 gallon and 74,810 gallon) areneeded in series to produce enough yeast propagation for a 469,423gallon yeast stage tank. TAB 20 compares alcohol percentage over time in7 and 10 fermenter systems for LT3FEM, LT4FEM, and current 7 and 10fermenter systems. This shows that a) an LT3FEM system cuts fermentationcycle time by 8 to 10 hours (8 hour for 7 fermenter systems and 10 hoursfor 10 fermenter systems) and b) an LT4FEM system cuts fermentationcycle time by 6 to 8 hours (6 hours for 7 fermenter systems, and 8 hoursfor 10 fermenter systems.) TAB 21 summarizes the amount of dry yeast,size of yeast slurry tank, size of yeast tank, and size of yeast stagetank for an LT4FEM system with various fermentation systems (between 4and 10 fermenters). TAB 22 shows the minimum necessary size for a yeaststage tank for LT2FEM, LT3FEM and LT4FFEM systems. Basically, theminimum size for a yeast stage tank is 3.33 times the mash intake rateper hour to achieve a 30% yeast propagation rate. For a 25% yeastpropagation rate the yeast stage tank must be 4 times the mash intakerate. For a 40% yeast propagation rate the yeast stage tank must be 2.5times the mash intake rate.

FIG. 7 illustrates a method 700 having a Continuous Yeast Propagation inYST or Fermenter in accordance with some embodiments. The system ofmethod 700 is embodied as LT5FEM (Continuous Yeast Propagation in YST orFermenter Method). The method 700 combines the systems of LT3FEM andLT4FEM. Both LT3FEM and LT4FEM are able to use less dry yeast. LT3FEMuses continuous yeast propagation in a large yeast tank to feed multiplefermenters. LT4FEM recycles yeast solution by sending the solution fromone fermenter to the next in line. These methods and systemssignificantly decrease capital and operational costs by reducing the dryyeast needed, and shortening the time for a full fermentation cycle.Recycling the yeast in these ways can increase the chance of infection.

However, field data suggests that it is safe to complete two passes ofactive yeast solution from a yeast stage tank 702 to a fermenter 706 ortwo passes from one fermenter 704 to another fermenter 706; or one passfrom a yeast stage tank 702 to a fermenter 704/706 and one pass from onefermenter 704 to another fermenter 706 with this method before startinga new fermentation cycle. TAB 23 shows simulation data for a 7 fermentersystem with one pass from yeast stage tank 702 to fermenter 706 usingLT3FEM technology of continuous propagation in a minimum size yeaststage tank 702 (589,223 gallons) followed by one recycling pass usingLT4FEM technology of recycling yeast solution which sends solution fromone fermenter to another. TAB 24 shows simulation data for a 7 fermentersystem with one pass (from yeast stage tank to fermenter) using LT3FEMwith a maximum size yeast stage tank (789,990 gallons) followed by onerecycling pass (from fermenter to fermenter) using the LT4FEM recyclingmethod. This data shows that the larger yeast stage tank cutsfermentation time and decreases the chance of infection.

TAB 15 shows data for one pass using the LT3FEM method of continuousyeast propagation in a yeast stage tank and TAB 19 shows one recyclingpass using the LT4FEM method of recycling solution from fermenter tofermenter. TAB 25 shows two passes with the first pass using LT3FEMtechnology (from yeast stage tank to fermenter) and the second passusing LT4FEM technology (fermenter to fermenter). TAB 26 shows tworecycling passes using the LT4FEM set up of recycling yeast solution fora 10 fermenter system. TAB 27 shows two passes using the continuousyeast propagation setup of LT3FEM for a 10-fermenter system. The datashows that more passes using these technologies results in greaterdecreases to capital and operational costs, but can increase the chanceof infection.

FIG. 8 illustrates a method 800 having a Fermenter Tank used as YST inaccordance with some embodiments. The system of method 800 is embodiedas LT6FEM (Fermenter Tank used as YST Method). In some embodiments, theabove systems (LT1FEM to LT5FEM) all used one or more larger yeast stagetanks between the yeast tank and the fermenters. These systems candecrease capital costs, operational costs, and the work for operators tofill, dump and Clean-In-Place (CIP). FIG. 8 shows a yeast stage tankperforming one pass of continuous yeast propagation to a fermenter. Insome embodiments, this operation can continue for multiple passes. Morepasses increase savings in operational and capital costs, but alsoincreases the chance of infection.

FIG. 9 shows a fermenter 902, which performs a continue yeastpropagation twice for the fermenter 904 and 906. The fermenter 908performs continue yeast propagate twice for fermenter 910 and 912.

FIG. 10 show a fermenter 1002, which performs a continue yeastpropagation to fermenter 1004, which is followed by yeast recycling fromthe fermenter 1004 to fermenter 1006. The ferment 1008 performs continueyeast propagation for fermenter 1010 followed by yeast recycling fromfermenter 1010 to fermenter 1012.

The above FIGS. 8-10 illustrate some embodiments using one or morefermenters as the yeast stage tank (e.g., can be named as a fermenter asa yeast stage tank or “FYST”). In such cases, using the fermenter toperform the processes and functions of a yeast stage tank (e.g., yeastpropagation), so that no additional yeast stage tank is needed. A yeastsolution is first transferred from a yeast tank to the FYST. The yeastsolution in the FYST is propagated to become a propagated solution. Insome embodiments, the propagated yeast solution is continuouslytransferred from the one or more of FYST to one or more fermenters. Inother embodiments, the propagated yeast solution is continuouslytransferred from the FYST to first fermenter and then transfers thesolution from the first fermenter to the second or subsequentfermenters, which is referred as a recycling yeast process. Variousprocesses paths and procedures are within the scope of the presentdisclosure.

In some embodiments, LT6FEM (the method 800) uses a fermenter 802 as ayeast stage tank to continuously propagate yeast for the next fermenter804. Once the first fermenter 802 (donator fermenter) has suppliedenough ideal yeast solution to the second fermenter 804 (receptorfermenter), then the first fermenter 802 stops acting as a yeast stagetank, and then the fermenter 802 is filled completely with mash andstarts fermenting.

TAB 28 shows simulation data for a four fermenter system. Fermenters #1802 and #3 806 are used as yeast stage tanks and propagate yeast tosupply huge amounts of yeast solution for fermenters #2 804 and #4 806.Once done, Fermenters #1 802 and #3 806 are filled up with mash and actas fermenters. This allows the fermentation cycle to be complete in 48hours. As shown in TAB 28, 6.46 pounds of dry yeast are added to 155gallons of water in the yeast slurry tank with nutrients for two hours.This solution is then dumped to a 20,000 gallon yeast tank where mash isadded at a rate to increase the total volume by 18.2 percent per hour(see cell C9:C38). This rate maintains the yeast cell count at a maximum(250*10″6).

After 32 hours of yeast propagation time, the yeast tank contains 19,781gallons of ideal yeast cell count solution. This yeast solution with amaximum yeast cell count (250*10{circumflex over ( )}6) is dumped toFermenter #1 802 and mash is added to increase volume by 18 percent perhour. This allows the yeast cell count to remain ideal. After 16 hoursthe total volume in fermenter #1 802 will be 281,135 gallons (seeH7:H22). Fermenter #1 802 acts like a yeast stage tank by continuouslypropagating yeast for another 16 hours to supply a huge amount of idealyeast solution to fermenter #2 (see cell H23:H38, M23:M38). Thenfermenter #1 802 fills up with mash and acts as a fermenter (see cellH39:H54). During this filling up period fermenter #3 806 will startacting as a new yeast stage tank (see cell R39:R54).

TAB 28 shows a yeast stage tank doing one pass of continuous yeastpropagation to a fermenter. However, this operation can continue formultiple passes. More passes increases savings in operational andcapital costs but also increases the chance of infection. TAB 28A showsthe LT6FEM system cuts alcohol production lag time by around 10 hours.Thus, the LT6FEM system can operate on a 48-hour (2 day) fermentationcycle instead of the current 56 hour cycle. TAB 28 also shows that witha 20,000 gallon yeast tank, the LT6FEM system can maintain maximum yeastcell count for any yeast that has a yeast growth rate over 18.2 percentper hour. Normal yeast growth rate is around 25 to 30 percent.

The LT6FEM simulation data for 4 to 10 fermenter systems with fillingtimes between 5 and 16 hours, variable yeast tank sizes, and differentyeast growth rates is summarized in TAB 29. For a current 7 fermentersystem (800,000 gallon tanks) with 8 hour filling time, the mash intakerate is 100,000 gallons per hour (GPH). For a yeast growth rate of 30%(see cellD16:C22), the minimum yeast tank size is 40,000 gallons(0.4*100,000) and the minimum yeast stage tank capacity is 329,000gallons (3.29*100,000). If yeast growth rate is only 25%, like typicalGMO yeast, then the yeast tank must be 65,000 gallons (0.65*2100,000)and yeast stage tank capacity is 386,000 gallons (3.86*100,000).Clearly, a larger yeast tank is needed for lower yeast growth rateunless a new system is designed like the LT6FEM system.

Using the LT6FEM method for a 8 fermenter system with 7 hour fillingtime, it is able to be operated it like 2 four fermenter systems with 14hour filling times but staggered by 7 hours. Similarly, a 10 fermentersystem with 5.5 hour filling times can operate as two 5 fermentersystems with 11 hour filling times but staggered by 5.5 hours. The splitmash flow concept used in LT1FEM can also be incorporated into LT6FEM.TAB 29 compares results for 8 fermenter systems (cell E13:I22 againstcell F24:I32), and ten fermenter systems (cell B24:E33 against cellJ24:M33). TAB 29 also shows that treating 8 and 10 fermenter systems astwo 4 and 5 fermenter systems allows the use of a smaller yeast tank butleads to lower alcohol percentage and requires longer fermentation time.

TAB 30 shows the alcohol percentage in the fermenter during the first 18hours and shows that higher alcohol contents achieved with larger yeasttanks and yeast stage tanks. TAB 31 shows yeast tank sizes needed forvarious filling times and yeast growth rates. Larger yeast tanks areneeded where the yeast growth rate is slower or where filling time isshorter. TAB 32 shows the yeast stage tank size needed for variousfilling times and yeast growth rates. Larger yeast stage tanks areneeded where yeast growth rate is slower or where filling time isshorter. The maximum size of a yeast stage tank is the same as the sizeof a fermenter tank.

TAB 33 shows average alcohol percentage at hour 18 based on variousfilling times and yeast growth rates. Lower yeast growth rates andshorter filling times require a larger yeast tank and yeast stage tankto increase alcohol percentage in the fermenter.

TAB 34 shows the fermentation time reduced by 6 to 17 hours depending onthe size of the yeast tank and yeast stage tank. Maximum yeast tank sizeand maximum yeast stage tank size (same size as fermenter) will give theshortest fermentation time cutting fermentation time by 17 hours for a 4fermenter system and by 13 hours for a 10 fermenter system. TAB 35 showsthe amount of dry yeast needed dependent on filling times and yeastgrowth rates. More dry yeast is needed for shorter filling times orslower yeast growth rates.

The above analysis is based on fermenter systems where the yeast stagetank acts as a continuous yeast propagation tank and supplies hugeamounts of ideal yeast solution for one pass. However, when more thanone pass can be completed/performed without infection problems, furtherdecreasing operational costs are achieved. Factors like system design,bacterial control, type of yeast, and operational conditions determinehow many passes can be completed without significantly increasing therisk of infection. More passes using continuous yeast propagationincrease savings in yeast propagation cost and enzyme cost.

TAB 36 compares alcohol percentage in a 7 fermenter system afterdifferent numbers of passes. TAB 37 compares the alcohol percentage athour 18 in a 7 fermenter system relative to the amount of dry yeast usedthe number of passes. The data shows that an LT6FEM system using amaximum size yeast tank and maximum size yeast stage tank for multiplepasses is ideal. LT6FEM benefits include: a) it produces less unwantedbyproducts like glycerol (less than 1% glycerol when finished withfermentation), b) it increases alcohol yield by up to 3% over currentbatch systems, c) it decreases bacterial infection problems, d) itstabilizes operation, leading to less variability, e) it decreases yeastpropagation costs by more than 90%, and f) it decreases enzyme costs bymore than 30%.

The data shows that a larger yeast stage tank gives better results andleads to a more stable operation. But this solution requires a largeryeast tank and more dry yeast. For an LT6FEM system, the maximum yeaststage tank size is the same as the fermenter tank size. TAB 38 shows theyeast tank size needed for a maximum size yeast stage tank depending onthe yeast growth rate. TAB 39 shows the average alcohol percentage athour 18 for various yeast growth rates when the yeast stage tank is thesame size as a fermenter. TAB 40 shows the decrease in fermentation timeneeded for various yeast growth rates when a maximum size yeast stagetank is used. TAB 41 shows the amount of dry yeast needed for variousyeast growth rates when a maximum size yeast stage tank is used.

TAB 29 to TAB 35 show the minimum yeast stage tank size needed tomaintain the ideal yeast cell count at all times. TAB 38 to TAB 41 showresults for a maximum size yeast stage tank (same size as a fermentertank). The LT6FEM system improves operation with a yeast stage tank thatis between the minimum and maximum size detailed. The impact of theyeast stage tank size depends on the size of the yeast tank (amount ofyeast solution sent to the yeast stage tank). An additional benefit ofthis technology is operation stability. Yeast growth rate can varygreatly but the LT6FEM system works even with lower yeast growth rates.Slower yeast growth stabilizes operation, decreases chance of infection,and decreases chance of yeast stress.

For very large fermentation systems, such as the typical ICM 8 to 10fermenter systems, the filling time is very short (5 to 7 hours). Thus,there is not enough time for the yeast tank and the yeast stage tank toprovide a sufficient volume of the ideal yeast cell count solution tothe next fermenter. LT6FEM solves this problem by treating the system astwo or even three smaller systems. For example, TAB 42 shows that thetypical ICM 10F5H system (10 fermenter system with a 5 hour fillingtime) can operate as two 5 fermenter systems with 12 hour filling timesas shown in program 22LTtwo5F12H1P0.3 5.73 0.28 or three 3 fermentersystems are able to be formed with 18 hour filling times as shown inprogram 22LTthree 3F18H2P0.44 11.7 0.2.

Increasing fill time allows the use of smaller yeast tanks and yeaststage tanks. The Lee Tech Fermentation Simulator can consider all thevariables and optimize any customer's fermentation system. The Simulatorshows that there are some optimum relationships between the size of theyeast tank, the yeast stage tank and fermentation time. The Lee TechFermentation Simulation program is a very useful tool for finding theoptimum fermentation system for any customer.

The above six LTFEM technologies (LT1FEM to LT6FEM) have differentadvantages and disadvantages. Each system is ideal for meeting specificchallenges in existing fermentation systems. However, the best system isLT6FEM which has the greatest reduction in operational and capitalcosts. In the disclosure, the term LT # FEM refers to the type number ofexemplary embodiments. In some embodiments, the fermenters can be splitinto two or more groups. In some embodiments, 10 fermenters with fillingtime of 5.5 hours can be split into two 5 fermenter tanks (e.g., inparallel lines) with filling time of 11 hours. In a case of 9 fermentertanks, three lines of 3 fermenter tanks each line. Any other manners ofsplitting the total number of fermenter tanks are within the scope ofthe present disclosure.

Using continuous yeast propagation or yeast recycling methods to getlarge amounts of yeast solution to a fermenter has been described in aprevious patent application, U.S. Provisional Patent Application Ser.No. 62/044,092, filed Aug. 29, 2014 and titled, “NEW IMPROVEMENTFERMENTATION SYSTEM FOR DRY MILL PROCESS”. However, without a largeyeast stage tank, the yeast cell count (YCC) in the 1st fermenter (ordonator fermenter) drops too low causing yeast stress (which can resultin unwanted byproducts like glycerol) and bacterial infections(resulting in another unwanted byproduct, lactic acid). Larger yeaststage tanks need more time to reach the ideal YCC solution. As shown,combining continuous yeast propagation or yeast recycling with a largeyeast stage tank decreases operational and capital costs. The computersimulation can show the optimal yeast propagation strategies, yeast tanksizes and quantity, yeast stage tank size and design, and the amount ofdry yeast needed. This detailed information is extremely useful forevery dry mill plant.

The purpose of splitting the mash flow is ensuring the yeast cell countin the yeast tank and fermenter tanks have a maximum yeast cell count(>250*10{circumflex over ( )}6) and maintain a higher percentage ofalcohol to suppress bacterial growth.

In utilization, the methods and systems disclosed herein are used toprovide an optimized yeast solution to the fermentation tanks forfermentation processes.

In operation, a yeast stage tank is used to prepare the yeast solutionto a predetermined condition before adding to the fermenters.

What is claimed is:
 1. A fermentation process using a yeast stage tankcomprising: a. transferring a first yeast solution having a yeastcontent less than 5 g weight per liter from a yeast tank to the yeaststage tank; b. continuously adding mash and maintaining a maximizedyeast cell count greater than 250*10{circumflex over ( )}6 cells/ml inthe yeast stage tank for an entire filling period; c. using the yeaststage tank as a continuing yeast propagation tank to produce apropagated active yeast solution for a fermenter tank during the fillingperiod to maintain the maximized yeast cell count in both the yeaststage tank and the fermenter tank; and d. transferring the propagatedactive yeast solution from the yeast stage tank to the fermenter tankwhen the transferring of the propagated active yeast solution results ina yeast cell count greater than 250*10{circumflex over ( )}6 cells/ml inboth the yeast stage tank and the fermenter tank for the entire fillingperiod.
 2. The fermentation process of claim 1, further comprisingcontinuously transferring the propagated active yeast solution from theyeast stage tank to multiple fermenter tanks.
 3. The fermentationprocess of claim 1, further comprising dumping an entire batch of aremaining propagated active yeast solution from the yeast stage tank toa coming fermenter tank after a predetermined number of fermenter tanksare full.
 4. The fermentation process of claim 3, further comprisingperforming a clean-in-place (CIP) process after the dumping the entirebatch of the remaining propagated active yeast solution to the comingfermenter tank.
 5. The fermentation process of claim 4, furthercomprising intaking a second yeast solution from the yeast tank to theyeast stage tank and restarting propagating the second yeast solution inthe yeast stage tank.
 6. The fermentation process of claim 1, whereinthe yeast stage tank has a size sufficiently large to maintain a yeastcell count>250*10{circumflex over ( )}6 cells/ml for an entire fillingprocess in both the yeast stage tank and the fermenter tank.
 7. Thefermentation process of claim 1, wherein the yeast stage tank has asize, which is provided as a function of a yeast propagation rate and amash supplying rate.
 8. The fermentation process of claim 7, wherein thesize of the yeast stage tank is at least 3.3 times of an hourly mashsupplying amount when a cell count of a yeast increases 30% per hour. 9.The fermentation process of claim 7, wherein the size of the yeast stagetank is at least 4 times of an hourly mash supplying amount when a cellcount of a yeast increases 25% per hour.
 10. The fermentation process ofclaim 1, further comprising keeping a food-to-yeast ratio represented bya formula of % DT/% yeast by weight below 4 for the entire fillingperiod of the yeast stage tank.
 11. The fermentation process of claim10, further comprising keeping a glucose level below 2% during theentire filling period of the yeast stage tank.
 12. The fermentationprocess of claim 1, wherein propagating the first yeast solution in theyeast stage tank to the propagated active yeast solution resulted in areduced needed amount of a yeast from the yeast tank.